1. Field of the Invention
The invention relates to a device and a method for wet treating a flat plate-like substrate, such as semiconductor wafers, flat panel displays or compact discs. The device comprising a spin-chuck for holding and rotating the substrate, at least one dispenser for dispensing a liquid onto at least one surface of said substrate, a liquid collector circumferentially surrounding said spin-chuck for collecting liquid, which is spun off the substrate during rotation. The liquid collector has at least two collector levels. Each of the collector levels has the purpose of separately collecting liquids in different collectors.
The device further comprises lifting means for moving spin-chuck relative to liquid collector substantially along the rotation axis and at least two exhaust levels for separately collecting gas from the interior of the liquid collector. Collecting gas from the interior of the liquid collector is useful to avoid deposition of mist being generated when liquid is spun off the substrate.
2. Description of Related Art
Such a liquid collector often is called a “cup” even though it does not necessarily have a closed bottom. Another word often used for the liquid collector is “chamber” even though it is not closed on all sides.
Such a device is known in the art and described in details in U.S. Pat. No. 4,903,717. This patent shows each collector of each collector level being connected to a common exhaust. Each collector level thereby simultaneously serves as an exhaust level. Therefore while the common exhaust is turned on gas is sucked from the interior of the liquid collector by each exhaust level.
During processing it might happen that below the level of the spin-chuck the gas pressure is lower than ambient gas pressure. Consequently liquid which is ought to be spun in to a specific collector level might be partly sucked into the collector level below the selected collector level.
If a liquid X is brought to a wrong collector level in which a different liquid Y shall be collected liquid X will contaminate liquid Y. In the worst case liquids X and Y react with one another generating hazardous or flammable reaction products.
Another undesired result might happen if liquid Y is recycled in order to treat as many substrates as possible. A contamination of liquid Y with liquid X then might result in the destruction of the substrates treated thereafter. In this case another consequence could be a significant decrease of the shelf life of liquid Y.